A() Data Independence: The ability to adjust a schema definition in one level without effecting a schema definition in next level is known as Data Independence.

There are two levels of data independence as following:

a() Physical Data Independence: The skill to modify the physical schema with no causing application programs to be rewritten.

b()  Logical Data Independence: The facility to modify the conceptual schema lacking causing
Application programs to be rewritten. Logical Data Independence is additional difficult to achieve than physical data independence because application programs are heavily dependent on the logical structure of the data they access.